Air conditioning



Jan 7 1941* R. A. WITTMANN 2,227,686

AIR CONDITIONING Filed Aug. 5, 1939 A Y 3 5 t:.

1 ss 2' l l 5I, I zo l l I I 5 I Ho z a. 11 .0 9 I N I CONDENSER sl l l ./'7 I I I l IE N Figa Tp- L d 5 nuentor Robmv' AIWimann sucTloN GAS TEMPERATURE IIE i# l I o a oo o ao a o0 0 THeoReTIcAL L2/Tom oF.REFR\c-ERAT|QN (itl Patented cEen.. i',

tipplication August 5, i939, Serial No. 288,6i5

2 laims.

This invention relates in general to air conditioning, and more particularly to automatic control-of systems of this character.

In the air conditioning art, it has 'become common to employ direct expansion coils for cooling air which is passed to a space being conditioned. In this type of system, compression type refrigu eration is generally used, the system having the usual compressor for compressing the refrigerant and a condenser for condensing the compressed refrigerant, the liquined refrigerant then passing through an expansion valve into the cooling coil wherein it evaporates, thus absorbing heat from the air passing over the coil.

One form of control for systems of this type consists of a thermostat for starting and stopping the compressor, the compressor operating at constant speed when in operation. With this type of control, the temperature ci the evaporating refrigerant in the cooling coil varies with the load upon the system. Thus during hot weather, the air passing over the cooling coil will be relatively hot which causes the refrigerant in the cooling coil to evaporate rapidly which in turn causes the pressureof the refrigerant therein to rise, thereby causing the temperature of the cooling coil to be relatively high. As the weather bea comes cooler, the refrigerant in the cooling coil will evaporate at a slower rate which permits the compressor to pump down the pressure to a lower value which causes the refrigerant to evaporate at lower temperature. Therefore with this type of system, the cooling coil operates at pro-n gressively lower temperatures as the cooling load upon the system decreases. While this type of system provides satisfactory results, it is defective from an economy standpoint due to the cooling coil temperature lowering at light loads. The power necessary for operating a cooling system is dependent upon the difference in levels between which the heat is transferred, that is, upon the diderence between the pressure at which the rerigerant evaporates in the evaporator and the pressure at which it ccndenses in the condenser. Therefore, the lower the pressure in the cooling coil, the more power required for producing the necessary cooling. Thus with a system of the type described, as the cooling load decreases, the cost of cooling per B. t. u. removed increases. This is entirely unnecessary for at such time the system could very easily carry the cooling load without increasing the' cooling capacity of the cooling coil as occurs when its temperature lowers.

Another type of control arrangement for direct expansion systems consists of a controller responding to the suction pressure of the refrigeration system, this controller acting to vary the speed or output of the compressor in a manner to maintain the temperature of the evaporator constant. This arrangement while avoiding increasing the cost of refrigeration at light loads and providing satisfactory results nevertheless fails to take advantage of light load conditions for actually securing lower cost refrigeration.

lt is an object of this invention to provide a. control system for an air conditioning system which acts to maintain proper conditions within a conditioned space, and which operates the system in -a manner to actually lower the cost of refrigeration as the load upon the system 15 decreases.

In accordance with this invention, the temperature of the cooling coil is actually increased as the cooling load on the system decreases. That is, the cooling coil is c'perated under maximum load 20 conditions at a minimum temperature for thereby securing the necessary cooling, and the temperature is progressively increased from the minimum value as -much as possible as the load decreases.

lt is a further object of this invention to provide a control system for air conditioning in which the eiect of the cooling coil upon the space is controlled in accordance with space temperature'as by placing it into and out of operation or varying the air ovv across such coil, and in which the temperature of the cooling coil is raised and lowered depending upon the load imposed upon the coil.

Another object of the invention is the provision of -a control system of the type just mentioned in which the temperature of the cooling coil is controlled by means of a device influenced by the heat content of the air discharged from the cooling coil, this device being preferably a wet bulb thermostat, or alternatively a dry bulb thermostat or a humidity responsive device.

Still another object oi this invention consists in the provision of an air conditioning control -sys tem in which the refrigeration system. is controlled by a device which acts to maintain the 45 cooling coil temperature constant, this device being reset or adjusted by a device responding to the condition of the air discharged from the cooling coil for raising the temperature of the cooling coil as the air conditioning load decreases. 50

A further object of the invention consists of a method of air conditioning control which causes.l raising of the cooling coil temperature as the load decreases.

Other objects of the invention will become apparent from the following description of the invention and the appended claims.

For a full disclosure of this invention reference is made to the following detailed description and to the accompanying drawing, in which Figure 1 illustrates diagrammatically one form c of the invention,

Figure 2 illustrates a modied form of the invention, and in which Figure 3 is a set of curves illustrating the function of the invention.

Referring to Figure 1 reference character I indicates an air conditioning chamber which may have a fresh air duct 2 and a return air duct 3 which leads from the enclosure being conditioned. This conditioning chamber Ialso connects to a fan 4 which draws the air through the chamber and discharges it through a duct 5 to the conditioned space. Located in the chamber I is a direct expansion cooling coil 6. This cooling coil forms a part of a refrigeration system which-includes'a compressor l, ya condenser 8, and an expansion valve 9 which is preferably of the thermostatic type having a control bulb I located on the discharge pipe II which leads from the outlet of the evaporator or cooling coil 6 to the inlet, of the compressor 1. The compressor 'I serves to compress refrigerant and to discharge it into the condenser 8 wherein it is condensed to liquid form, this liquid refrigerant then passing through the expansion valve 9 into the cooling coil 6 wherein it evaporates into the gaseous state thus absorbing heat from the air passing over the cooling coil, this gaseous refrigerant then passing through the suction line I I back to the compressor.

The compressor 'I is driven by any suitable means and preferably may be driven by means of an internal combustion engine I2. This engine may be of usual form having an exhaust manifold I3 and an intake manifold I4, a starting motor I and a starting motor relay and ignition circuit generally indicated as I6. This apparatus includes the usual ignition system for an internal combustion engine and also an automatic starting relay for the Lstarting motor I5 which may be of any suitable type such for example as that shown in the L. K. Loehr et al. Patent No. 1,773,913. This engine I2 is connected to the compressor i through any suitable unloading device I8 which may be a centrifugal clutch which permits the engine to start in an unloaded condition and which connects the engine to the compressor after the engine is rotating at or above a predetermined speed.

The starting and ignition apparatus I6 is controlled by means of a thermctat 26 which may be of the remote bulb type having a bulb 2I located in the return air duct 3 so as to respond to the temperature of the air in the conditioned space.

This thermostat is of the two-position type havingan electric switch which is closed when the space temperature rises to a predetermined value such as 75 F., this switch opening when the space temperature falls below this value. This thermostat is connected to the starting and ignition apparatus I6 and serves to energize the ignition for the engine and also the relay controlling the starting motor I5 when this switch is closed. This will cause rotation of the engine by the starting motor I 5 and when the engine starts the starting relay will deenergize the starting motor I5. The engine will then run until the space temperature falls to the value at which the thermostatic switch opens, this acting to deenergize the engine ignition system for stopping the engine. The thermostat 20 therefore serves to start the engine when space temperature rises above 75 F. While stopping the engine when the space temperature falls below this value. Of course this value is illustrative only and may be varied as desired without departing from the invention.

The speed of the engine I2 is controlled by means of a throttle valve 25 which may control the iiow of fuel to the engine. This valve is positioned by means of an electric proportioning motor 26 which may be of the type shown in the Taylor Patent 2,028,110. This proportioning motor is controlled by means of a suction pressure controller generally indicated as 21, and is also controlled by means of a wet bulbl discharge thermostat 28. Referring again to the proportioning motor 26 this motor is provided with a three-wire control circuit having terminals indicatedas R, W, and B, and is adapted to assume intermediate positions depending upon the relative values of resistance connected between terminals R and W and between terminals R and B. For example, if equal Values of resistance are connected between terminals R and W and between terminals R and B, the motor will assume the intermediate position in which the throttle valve is half open. However, if the resistance between terminals R and B is decreased without corresponding decrease in resistance between terminals R and W, the motor will operate to a new position in which the throttle valve is open widen. the position being proportionate to the new relationship between the resistances connected across these terminals. Conversely if the resistance between terminals R and W is decreased without corresponding decrease in resistance between terminals R and B, the motor 26 will rotate to a position in which the throttle valve 25 is closed to a greater extent.

Referring to the suction pressure controller 21, this controller may consist of a bellows 30 which is connected to the suction line II by means of a tube 3l. 'I'his bellows actuates a pivoted arm 32 which is biased by means of a spring 33, this arm 32 actuating a slider 34 which cooperates with a resistance 35 to form a control potentiometer for the motor 26. This arm 32 also actuates a corrector arm 3l which cooperates with a centertapped corrector resistance 38 which serves to make the control of the motor 26 by the controller 2 more uniform. 'Ihe right hand end of resistance35 is connected to terminal W of the motor 26 by wires 39 and 40, while the left hand end of this resistance is connected to terminal B of the motor by wires 4I and 42. The corrector resistance 38 is connected to terminal R of motor 25 by Wire 53. Thus the slider 34 of controller 2l is connected to terminal R of motor 26 through the slider 31, corrector resistance 38 and wire 43.

Assuming that the suction pressure or temperature of the cooling coil 6 is at an intermediate value, the slider 34 will engage the center of resistance 35 which serves to connect the left hand half of this resistance between terminals R and B while connecting the right hand half between terminals R and W. This will cause the throttle valve 25 to assume half open position for operating the engine at intermediate speed. If the suction pressure should increase, the bellows 3U will expand against spring 33 an amount proportionate to the increase in suction pressure, thereby causing the slider 34 to move to the left across resistance 35 which decreases the portion of the resistance 35 between terminals R and B while increasing the portion of this resistance acer/,ooo

between terminals R and W. This will cause the motor 2li to open the throttle valve 2o wider for increasing the engine speed. Therefore as the suction pressure increases due to the load upon the cooling coil fi increasing, the compressor speed will be increased tor carrying the .additional load. lit will ce apparent that upon decrease in suction pressure due to reduction in load upon the cooling coil li, the controls de scribed will operate in the opposite manner for decreasing the speed of engine l2. The suction pressure controller 2l therefore serves to vary the engine speed in a manner to just carry the load upon the cooling coil (i, serving to ,maintain the temperature of this cooling coil substantially constant.

Referring to the thermostat i@ this thermostat is provided for adjusting the control point of the suction pressure controller il in a manner to maintain a constant wet bulb temperature of the air leaving the cooling coil il.. This thermostat is diagrammatically illustrated as including a bellows lli which actuates an arm tl attached to a biasing spring This arm @l actuates a slider @which cooperates with a resistance lill for forming a compensating'potentiometer for the proportioning motor tti, The bellows it is attached by a capillary tulle 5l to a control bulb located at the outlet of the cooling coil il, this control bulb being covered by a wiclr 5t which is maintained wet by means of a water pan at. The pressure in the bellows il@ therefore varies in accordance with the wet bulb temperature of the air being discharged from the cooling coil o.

' The right hand end of the resistance t@ is conuecteol to terminal W of motor te by wires 5e and tu, while the left hand end ci this resistance is connected to terminal B by wires il@ and llt. The slider it is connected to terminal R by means of wire lill, a'cljusting rheostat titl, wire at.

and wire lit. v

Assuming that the load upon the air conditioning system increasesfthat is, the temperature of the air passing over the cooling coil t increases, the temperature or the air leaving the cooling coil t will rise thereby causing enpansion of the bellows for shifting the slider i@ to theleft across resistance 5Fl. This will decrease the portion of the resistance til which is connected between terminals it and B oi motor 2t, while increasing the portion connected loetween terminals R. and W. LThis action will cause the motor l@ to increase the opening of throttle valve 2b for thereby increasing the engine speed. lt will be noted that this increase in engine speed occurs over and above any increase in speed caused by the suction pressure controller 2l. speedcaused by the controller at will cause the suction pressure to begin falling and in response to this iall in suction pressure the suction pressure controller 2l will begin slowing down the engine speed until a point is reached wherein the suction pressure remains constant. Thus the action of the controller it in response to an increase in temperature of the air leaving the cooling coil is to in euect adjust the suction pressure controller 2l so as to maintain a lower suction pressure and consequently lower temperature oi the cooling coil t. it will be apparent that upon decrease in temperature of the` discharge air, the controller 2t will act in the opposite manner for increasing the value of suction pressure maintained by the suction pressure controller il. l

Therefore the increased engine The rheostat it serves to vary the euect oi the thermostat 2u upon the control point oi the controller El, and by properly adiusting tins rheostat the thermostat 2t may be made to varythe coil temperature `iust the proper amount for maintaining a constant discharge air temperature. For a more complete disclosure ci the compensated control circuit for the proportioning motor reference is made to the copcneiing application to John E. Haines, rial No. titulo, nieu September 3, i935, now matured into Patent No. 2,173,33Lissued September 19, 11.939.

Referring now to the operation oi the system as a whole, when the space temperature is below the thermostat 2li will cause the engine it to be at rest and therefore no cooling ci the space will occur. When the space temperature rises above the control point of thermostat to, this thermostat will place the engine into operation, and the speed at which this engine operates will be determined by the suction pressure controller 2l and its compensating controller it. Under maximum load conditions, the temperature of the air over the cooling coil will be at a maximum which causes the wet bulhtemperatureof the air discharging from the cooling coil to be at a maximum which will cause the thermostat 2li to adjust the suction pressure controller 2l for maintaining the cooling coil temperature at a minimum temperature for securing the necessary amount oi cooling. At this time the refrigerant in the evaporator will evaporate at a high rate, thus causing the suction pressure to be high as compared with the adjustment of the suction pressure controller ll by thermostat it, and consequently the engine will operate at full speed. As the load upon the system decreases, that is, the temperature or quantity oi the air passing over the cooling coil decreases, two reactions will occur. For one thing the wet bulb temperature of the air leaving the coil will decrease which will cause the controller it to raise the control point of the suction pressure controller 2l. Also less refrigerant will lne evaporated in the cooling coil t, which will cause the suction pressure to fall. The suction pressure controller El will thus slow down the engine il to a point at which the suction pressure rises to the new setting or the suction pressure controller il. Therefore as the load upon thesystem decreases, the suction pressure controller is reset to maintain a higher coil temperature and this controller will slow down the engine until the suction pressure rises to the new setting required by the discharge thermostat. inasmuch as less cooling is necessary as the load decreases, it follows that the temperature of the cooling coil t may be increased while still obtaining the necessary cooling action. This positive increasing of the cooling coil temperature as the load on the system-decreases reduces the operating cost of the system.

rlhis savings in operating costs by raising the coil temperature in the manner specined is illustrated in Figure 3. Referring to this ligure theload in tous of refrigeration are plotted as the ordinates of the graph, while the suction gas temperature is plotted as the abscissa. The theoretical horse power per ton of refrigeration varies in proportion to the suction gas temperature and this is also indicated. On this graph are the full line curves, a, b, c; and d which.

represent diuerentv'alues'of the air condition. Thus curve o represents the condition at 10G" F. dry bulbwet buluand curves bfc, and al Eil represent progressively lower temperature conil l ditions of the air.

curves e, f, g, h, and i, which represent different lns yThis graph also contains compressor speeds. It should be noted that these latter curves indicate that the suction gas temperature lowers upon decrease in load if the compressor is operated at constant speed. For

example, if the compressor is operated at 500 R. P. M. and the air is 100 dry bulb- 80 Wet bulb, the suction gas temperature resulting is illustrated at the intersection of curves a and e which is approximately 39 F. Now if the air temperature 'falls to 95 dry bulb-757 wet bulb the suction gas temperature will be that indicated at' the intersection of curves e and b which is 35. Therefore as pointed out before, if a compressor operates at constant speed, the suction gas temperature falls as the load upon the cooling coil decreases which causes the power required per ton of refrigeration to increase.

If the thermostat 28 is set to maintain a discharge temperature of 63 wet-bulb the action of the system would be as indicated by curve k. Thus if the air condition is 100 dry bulb-80 wet bulb, the suction gas temperature will be 39. If the air temperature falls to 95 dry bulbwet bulb, the suction gas temperature will be that indicated at the intersection of curves Ic and b which is approximately 47. Similarly upon further decrease in the air temperature, the temperature of the evaporator will rise and this will, as indicated, reduce the power required per ton of refrigeration and thereby secure a substantial savings in operating costs.

A In this connection it must be remembered that vdecided reduction in operating expenses during the major portion of the cooling season.

In some cases it may be desired to control the temperature in the space by means of dampers controlling the ow of air across the cooling coil so as to avoid the use of on-oif type control as in Figure 1. In such cases the arrangement shown in Figure 2 may be utilized. Referring to this figure the conditioning chamber la is provided with a by-pass around the cooling coil 6a and the ow of air through the by-pass and through the cooling coils is controlled by means of a bypass damper |00 and a face damper |0| which are positioned by means of a proportioning motor |02. This proportioning motor is in turn positioned by means of a potentiometer type return air thermostat |03, this thermostat serving to cause the motor |02 to position the dampers for increasing the flow of air through the cooling coil 6a upon rise in return air temperature While decreasing the flow of air through this coil upon fall in temperature. The proportioning motor |02 is additionally provided with an auxiliary switch |04, which switch is arranged so as to open whenever the face damper |0| becomes closed. This switch |04 is connected to the engine starting and ignition apparatus I6 and corresponds .to the thermostat 20 of Figure 1. The remainder of the system is exactly the same as in Figure 1 and accordingly is not described here. Like parts are provided with like reference numerals.

The operation of the system of Figure 2 is similar to that of Figure 1. When the space temperature is below the setting of thermostat |03, this thermostat causes the proportioning vents ilow of air across the cooling coil 6a. At

this time the auxiliary switch |04 is open and consequently the engine I2 is out of operation. As the space temperature begins rising within the control range of thermostat |03, this thermostat causes the damper motor |02 to begin opening the face damper |0| and to close the auxiliary switch |00 for starting the engine I6. The speed of the engine will now be controlled by the suction pressure controller 21 and the compensating wet bulb thermostat 28, which cause the motor 26 to position the throttle valve 25 in exactly the same manner as described in detail in connection with Figure l. It will be apparent that the arrangement of Figure 2 will modulate the temperature of the air supplied to the conditioned space in accordance with the temperature in the space for thereby maintaining a constant space temperature, and that during normal operation the controllers 2l and 28 will control the engine speed in accordance with the load actually applied to the cooling coil 6a.

From the foregoing description it will be apparent that this invention provides an air conditioning control system and method of control which maintains the temperature of a conditioned space at the desired value and which also adjusts the operation of the system so as to secure maximum economy with the equipment provided. While the invention is of particular utility in direct expansion type systems, as shown, it is not limited to systems of this type but is also applicable to indirect type of systems wherein chilled water or brine is passed through the cooling coil. While I have shown and described only two forms of my invention, it will be apparent that various changes may be made without departing from the scope of the invention. I therefore desire to be limited only by the scope of the appended claims.

I claim as my invention:

1. Inv an air conditioning system, in combination, a direct expansion cooling coil, means for passing air over said cooling coil and discharging it into'a space being conditioned, a compressor connected to said cooling coil, a variable speed prime mover for driving said compressor, means responsive to a condition of the air in said space which is aiected by said cooling coil for controlling the effect of said cooling coil upon the air in said space for thereby maintaining said space condition at the desired value, a speed controller for said prime mover, control means for said speed controller including a device influenced by the temperature of said cooling coil for varying the speed of said prime mover in a manner for maintaining the temperature of said cooling coil constant, adjusting means for adjusting the temperature of said cooling coil maintained by said control means, and means located in the air discharged from said cooling coil and iniiuenced by the heat content thereof for actuating said adjusting means in a manner t0 raise the temperature of the cooling coil upon decrease in said heat content and vice versa.

2. In an air conditioning system, in combination, a direct expansion cooling coil, means for passing air over said cooling coill and discharging it into a space being conditioned, a compressor connected to said cooling coil, a variable speed prime mover for driving said compressor, means responsive to a condition of the air in said space which is affected by said cooling coil for controlling the effect of said cooling coil upon the air in said space for thereby maintaining said space condition at the desired value, a speed controller for said prime mover, control means for said speed controller including a device influenced by the temperature of said cooling coil for varying the speed of said prime mover in a manner for maintaining the temperature of said cooling coil constant, adjusting means for adjusting the temperature of said cooling coil maintained by control means, and means located in the air discharged from said cooling coil and inuenced by the wet bulb temperature thereof for actuating said adjusting means in a manner to raise the temperature of the cooling coil upon decrease in said wet bulb temperature and vice versa.

ROBERT A. WITTMAN N. 

